Gimbals

ABSTRACT

A gimbal assembly for carrying a gyroscope rotor for spin about a z axis is described which has an inner boss (3), and outer ring (6), first and second gimbal frames (4 and 5) situated between the two, first outer pivots (8) pivoting the first frame (4) to the outer ring (6) about a y axis, second outer pivots (10) pivoting the second frame (5) to the outer ring (6) about an x axis, first inner pivots (11) pivoting the second frame (5) to the boss (3), and second inner pivots (9) pivoting the first frame to the boss (3) about the x axis, the gimbal frames (4 and 5) being interlaced one with another. 
     A preferred method of forming the inner boss (3), the outer ring (6), and the gimbal frames (4 and 5) from a billet of solid material is also described.

This invention relates to gimbals.

It is known to carry the rotor of a gyroscope on a single ormulti-gimbal arrangement in which the gimbal frames or rings areinterconnected by spring biassed pivots instead of free pivots, thespring biassing acting to oppose relative pivotal displacement of thegimbals, that is to say, acting in a torsional sense.

Defining x, y and z as mutually perpendicular rotor fixed andundisplaced axes, z being the spin axis, at a "tuned" speed of rotationN given by: ##EQU1## (where:

K_(x), K_(y) are spring constants of the pivots about x and y rotoraxes, respectively,

a, b and c are gimbal principle moments of inertia components about thex, y and z rotor axes, respectively, c being the polar moment, and

n is the n^(th) gimbal, i.e. the number of gimbals) it is found that thewind up torques from the spring biassed pivots and the dynamic reactiontorques from the motion of the gimbals, (n≧1), as the consequence of asteady case displacement about an input axis, cancel one another whenintegrated over each revolution such that there is a zero mean torqueapplied to the rotor. As such the rotor can be regarded as conditionallyfree (i.e. over a limited angle) at the "tuned" speed.

A gyroscope employing only one gimbal (n=1) is inherently sensitive toan applied angular input at a period 1/2 N whence the rotor experiencesa mean torque acting upon it over each revolution so causing agyroscopic drift due to an unbalance between the gimbal dynamic torqueand the wind up torques of the spring-biassed pivots, whereas, with twoor more gimbals (n≧2) it is possible to balance the latter by adjustingthe dynamic inertias (a+b-c)_(n) of the individual gimbals.

This balancing of spatial torque vectors can be likened to the problemof balancing electrical vectors, for example 180° apart (n=2); 120°apart (n=3) and so on. In theory two vectors (n=2) can only be balancedto zero provided they are in perfect anti-phase, where with three ormore (n=≧3) this restriction does not apply.

Mechanical complexity increases, however, with three gimbals or more;the present invention is concerned with double gimbals and has for anobjective the provision of a double gimbal assembly which attempts toattain the perfect anti-phase requirement by precise axis orthogonalityand by precise geometry.

The condition for 2 N (angular) cancellation with double gimbals isgiven below by: ##EQU2##

In practice the spring constants are fixed as built, and the gimbaldynamic inertias are adjusted to satisfy both the tuning condition givenby equation 1 and the equality demanded by equation 2 for 2 N (angular)cancellation.

Reference is made to the mutually perpendicular rotor fixed andundisplaced axes x, y and z throughout the specification and claims toaid description.

According to the present invention a gimbal assembly for carrying arotor for spin aout a z axis includes an inner member, an outer member,first and second frame members situated between the inner and outermembers, first outer pivot means pivoting the first frame member to theouter member about a y axis, second outer pivot means pivoting thesecond frame member to the outer member about an x axis, first innerpivot means pivoting the second frame member to the inner member aboutthe y axis, second inner pivot means pivoting the first frame member tothe inner member about the x axis, the front frame member comprising acontinuous periphery having opposed regions at the y axis outwardlydirected from the z axis on which the first outer pivot means arecarried, further opposed regions at the x axis inwardly directed towardthe z axis on which the second inner pivot means are carried, andbridging regions joining the outwardly and inwardly directed regions,the second frame member comprising a continuous periphery identical tothat of the first frame member having opposed regions at the x axisoutwardly directed from the z axis on which the second outer pivot meansare carried, further opposed regions at the y axis inwardly directedtoward the z axis on which the first inner pivot means are carried, andbridging regions joining the outwardly and inwardly directed regions,successive bridging regions of one frame member being formed toalternately cross over and cross under the bridging regions of theidentically formed other frame member so that the frame members areinterlaced. Preferably the pivot means include biassing means whichoppose relative pivotal displacement of those members pivoted together.

Preferably the gimbal assembly above described is formed from a billetof solid material with parallel end faces by a method including the notnecessarily sequential steps of:

forming between the end faces four identical inwardly extending borestwo along the y axis and two along the x axis to accept the first andsecond pivot means, respectively,

forming between the end faces four identical wedge shaped inwardlyextending slots equally spaced between and in the same plane as the xand y axes of a depth to leave a boss of solid material on the z axis toeventually form the inner member,

forming an outer annular slot co-axially with the z axis to eventuallyseparate the outer member from the frame members, fillets of materialbeing left to hold the partly formed billet rigidly in one piece,

forming from the outer annular slot four slots inwardly extending towardthe z axis equally spaced between the x and y axes of a length toprovide clearance between the first and second frame members,

forming an inner annular slot co-axially with the z axis to eventuallyseparate the frame members from the inner member, fillets of materialbeing left to hold the partly formed billet rigidly in one piece,

forming four identical inner apertures on a common radius from the zaxis, two lying on the x axis and two on the y axis to provide access toinner regions of the pivot means after insertion in their bores,

forming four identical outer apertures on a common radius from the zaxis, two lying on the x axis and two on the y axis to provide access toouter regions of the pivot means after insertion in their bores,

forming an intermediate annular slot between the inner and outer annularslots, again co-axially with the z-axis, the intermediate slot being infour identical segments two being equally spaced about the x axis andtwo being equally spaced about the y axis to provide eventual separationbetween the inwardly and outwardly directed regions of the first andsecond frame members,

inserting and anchoring pivot means in the four bores to provide pivotsbetween the inner member and the frame members and between the outermember and the frame members, and,

removing the fillets of solid material to release the frame members fromone another and from the outer and inner members.

Preferably the pivot means for both the inner and the outer pivots arein one piece for each of the four inwardly extending bores andsubsequent to insertion in each bore are separated to form the inner andouter pivot means.

One preferred example of a gimbal assembly according to the invention isillustrated with reference to the accompanying drawings in which:

FIG. 1 is an isometric view of a gimbal assembly,

FIG. 2 is an end view illustrating various manufacturing steps,

FIG. 3 a, b, c and d, illustrate various manufacturing steps for agimbal pivot means, and,

FIGS. 4 and 5 illustrate the incorporation of pivot means into a partlyformed billet and subsequent manufacturing steps.

Referring initially to FIG. 1 a gimbal assembly suitable for carrying agyroscope rotor, not shown, is formed from a billet of solid metal withthe addition of pivot means. The billet is of cylindrical form havingparallel end faces 1 and 2; the distance between the end faces 1 and 2(that is to say the length of the billet) is much less than itsdiameter.

For ease of description the longitudinal axis of the billet is termedthe z axis, this being the spin axis of the gyroscope rotor whenundisplaced, and two further axes are termed the x and y axes, being theaxes about which the rotor pivots when initially undisturbed.

All three axes are mutually perpendicular and the x and y axes lie inthe same plane.

The gimbal assembly is symmetrically arranged around the z axis; it isalso symmetrically arranged about both the X and Y axes.

The gimbal assembly has a central boss or inner member 3 through whichextends a bore 3a co-axially formed with the z axis.

The inner member carries first and second frame members 4 and 5,respectively, which themselves carry a mounting ring or outer member 6on pivot means to be described. The outer member is provided withscrewed holes 7. The outer member 6 is in the form of a completeannulus.

The first frame member 4 is pivoted to the outer member 6 about the Yaxis by first outer pivot means 8 and to the inner member 3 about the xaxis by second inner pivot means 9 whilst the second frame member 5 ispivoted to the outer member 6 about the x axis by second outer pivotmeans 10 and to the inner member 3 about the Y axis by first inner pivotmeans 11.

Both frame members 4 and 5 are of identical form and each comprise acontinuous periphery formed in one piece. That referenced 4 has opposedregions 12 and 13 outwardly directed from the z axis at the y axis onwhich the first outer pivot means 8 are carried, and opposed regions 14and 15 inwardly directed toward the z axis at the X axis on which thesecond inner pivot means 9 are carried. The regions 12 and 15 are joinedby a bridging region 16 which lies toward that end face referenced 1,the regions 15 and 13 are joined by a bridging region 17 which liestoward that end face referenced 2, the regions 13 and 14 are joined by abridging region 18 which lies toward the end face 1, and finally tocomplete the periphery, the regions 14 and 12 are joined by a bridgingregion 19 which lies toward the end face 2.

That frame member 5 has opposed regions 20 and 21 outwardly directedfrom the z axis at the x axis on which the second outer pivot means 10are carried, and opposed regions 22 and 23 inwardly directed toward thez axis at the y axis on which the first inner pivot means 11 arecarried. The regions 20 and 22 are joned by a bridging region 24 whichlies toward the face 1 and crosses over the bridging region 19 of theframe member 4, the regions 22 and 21 are joined by a bridging region 25which lies toward the face 2 and crosses under the bridging region 16 ofthe frame member 4, the regions 21 and 123 are joined by a bridgingregion 26 which lies toward the face 1 and crosses over the bridgingregion 17 of the frame member 4, and finally, to complete the periphery,the regions 23 and 20 are joined by a bridging region 27 which liestoward the face 2 and crosses under the bridging region 18 of the framemember 4. The frame members 4 and 5 are thus interlaced one withanother.

The pivot means are of the type which include biassing means whichoppose relative pivotal displacement of those members pivoted together.In this embodiment, the first and second outer pivot means 8 and 10, andthe first and second inner pivot means 11 and 9 are all identical;accordingly it suffices to describe just one example.

Each of said outer and inner pivot means has two spaced pivot unitscoaxially mounted on the x or the y axis on opposite sides of the zaxis.

Each pivot unit comprises a tubular body having one portion 28 and aseparated further portion 29 co-axially arranged, each portion having atongue 30 projecting toward the other portion and lying beside thetongue 30 of that other portion. Twin transverse leaf spring members 31extend between the tongues 30, the members 31 being axially spaced andset normally to one another in a cruciform arrangement.

The inner member 3, the frame members 4 and 5 and the outer member 6 areformed with bores 32 and 33 coincident with the y axis and bores 34 and35 coincident with the x axis in which the portions 28 and 29 of eachpivot unit are housed and are fixedly located.

Preferably the pivot units are formed as four sets of axially joinedpairs, each pair being inserted in one of the bores 32, 33, 34 or 35 andsubsequently separated. FIG. 3 refers.

Each pair, that is to say, a first outer pivot means 8 and a first innerpivot means 11, or a second outer pivot means 10 and a second innerpivot means 9, is formed of a tube 40 of a length chosen to extend fromthe inner, through the frames, to the outer member when inserted into abore 32, 33, 34 or 35.

The tube 40 is formed, as shown in FIG. 3b, with eight longitudinalslits 41 in two axially spaced sets of four. Each set of four has itsslits in two pairs oppositely opposed and set at 90° to one another.These slits 41 are for the location of the leaf spring members 31.

The tube is further formed with four longitudinal slits 42 in twoaxially spaced sets of two. In each set, the two slits are opposite oneanother. These slits are for eventual separation of the pivot units andform adjacent edges of the tongues 30.

The leaf spring members 31 have end portions 43 which are slotted toengage side edges of the slits 41 so that the spring members extendacross the interior of the tube from one of a pair of slits to theother. The leaf spring members are brazed in place as shown in FIG. 3d.

Referring now to FIG. 2, the inner member 3, the frames 4 and 5, and theouter member are conveniently formed from a cylindrical billet of solidmaterial. This has the two parallel end faces 1 and 2 equally spacedfrom the plane of the x and y axes.

The axial bore 3a is formed along the z axis and then the four inwardlyextending bores 32, 33 and 34, 35 are formed which will accept the pivotmeans.

Four wedge shaped inwardly extending slots 44 are then formed betweenthe end faces 1 and 2 equally spaced between and in the same plane asthe x and y axes. The slots extend inwardly to a depth which leaves aboss of solid material which will eventually form the inner member 3.

The four inwardly extending bores 32, 33 and 34, 35 extend into theinner member 3.

An outer annular slot 45 is formed co-axially with the z axis rightthrough the billet to eventually separate the outer member 6 from theframe members 4 and 5, fillets of material 46 being left to temporarilyhold the partly formed billet rigidly in one piece.

Four inwardly extending (i.e. toward the z axis) slots 47 are formedfrom the outer annular slot 45 equally spaced between the x and y axesof a length to provide clearance between the first and second framemembers 4 and 5.

An inner annular slot 48 is formed co-axially with the z axis toeventually separate the frame members 4 and 5 from the inner member 3,fillets of material 49 again being left to hold the partly formed billetrigidly in one piece.

Four identical inner apertures 50 are formed on a common radius from thez axis, two lying on the x axis and two on the y axis to provide inneraccess to the pivot means after insertion in the bores 32, 33 and 34,35.

Four identical outer apertures 51 are formed on a common radius from thez axis, two lying on the x axis and two on the y axis to provide outeraccess to the pivot means after insertion in the bores 32, 33 and 34,35.

An intermediate annular slot 52 is formed between the inner and outerannular slots 48 and 45, again co-axially with the z-axis, theintermediate slot being in four slot segments two being equally spacedabout the x axis and two being equally spaced about the y axis toprovide eventual separation between the inwardly and outwardly directedregions of the first and second frame members.

At this stage the four pairs of pivot units are inserted into the fourbores 32, 33 and 34, 35 so that the slits 42 lie in the apertures 50 and51. The regions of the tubes 40 which will on separation form theportions 28 and 29 are then brazed in position to their respectivemembers.

The tubes 40 are then cut transversly to the axis x or y, those cutsreferenced 53 and 54 extending from the periphery of the tube to theslits 42, that is to say extending only part way across the tubes toform the tongues 30, and those cuts referenced 55 extending fully acrossthe tubes to separate the inner from the outer pivot units of each pair.Access to allow the cuts 53 and 54 to be made is through the apertures50 and 51 whilst access for the cuts 55 are provided by the segments ofthe intermediate slot 52.

The inner member 3 and the frame members 4 and 5 are finally separatedby removal of the fillets 49, and the members 4 and 5 are finallyseparated from the outer member 6 by removal of the fillets 46.

At the same stage prior to final separation the frame members 4 and 5are provided with screw holders 56 and screws therein to allowadjustment of their dynamic inertias. As shown, the screw holders 56 aremounted upon cut away regions of the bridging regions 16 to 19 and 24 to27, respectively.

The forming and cutting of the various components is preferably effectedby a process such as spark machining. Any brazing or welding is effectedby electron beam processes.

Some advantages accrueing from the invention as described are asfollows:

1. The axes x, y and z can be precisely spatially aligned and the pivotmeans can be accurately positioned upon the x and the y axes.

2. The frames 4 and 5 can be symmetrically and identically formed sothat in effect each frame ghosts the other as the gimbal assemblyrotates to provide the effect of two mechanically identical gyroscopesspatially displaced by a period of one quarter of one revolution.

3. Rotor mechanical noise (due to swashing and coning) is reduced suchthat a useful improvement in pick-off resolution can be achieved withthe result of yet further reducing any residual rotor offset and elasticrestraint drift errors.

4. The gimbal assembly provides a high rejection of any 2 N angularvibration input.

5. The overall manufacturing costs can be accurately forecast andmaintained since the forming operations rely in the main uponprogrammable machining operations rather than the variable assemblyskills of personnel.

We claim:
 1. A gimbal assembly for carrying a rotor for spin about a z axis includes an inner member, an outer member, first and second frame members situated between the inner and outer members, first outer pivot means pivoting the first frame member to the outer member about a y axis, second outer pivot means pivoting the second frame member to the outer member about an x axis, first inner pivot means pivoting the second frame member to the inner member about the y axis, second inner pivot means pivoting the first frame member to the inner member about the x axis, the first frame member comprising a continuous periphery having opposed regions at the y axis outwardly directed from the z axis on which the first outer pivot means are carried, further opposed regions at the x axis inwardly directed toward the z axis on which the second inner pivot means are carried, and bridging regions joining the outwardly and inwardly directed regions, the second frame member comprising a continuous periphery identical to that of the first frame member having opposed regions at the x axis outwardly directed from the z axis on which the second outer pivot means are carried, further opposed regions at the y axis inwardly directed toward the z axis on which the first inner pivot means are carried, and bridging regions joining the outwardly and inwardly directed regions, successive bridging regions of one frame member being formed to alternately cross over and cross under the bridging regions of the identically formed other frame member so that the frame members are interlaced.
 2. A gimbal assembly according to claim 1 wherein the pivot means include biassing means which oppose relative pivotal displacement of the pivoted members.
 3. A gimbal assembly according to claim 2 wherein the biassing means include leaf spring members which extend for flexure between the pivoted members.
 4. A method of forming a gimbal assembly as defined in claim 1 from a billet of solid material with parallel end faces, including the not necessarily sequential steps of:forming between the end faces four identical inwardly extending bores two along the y axis and two along the x axis to accept the first and second pivot means respectively, forming between the end faces four identical wedge shaped inwardly extending slots equally spaced between and in the same plane as the x and y axes of a depth to leave a boss of solid material on the z axis to eventually form the inner member, forming an outer annular slot co-axially with the z axis to eventually separate the outer member from the frame members, fillets of material being left to hold the partly formed billet rigidly in one piece, forming from the outer annular slot four identical slots inwardly extending toward the z axis equally spaced between the x and y axes of a length to provide clearance between the first and second frame members, forming an inner annular slot co-axially with the z axis to eventually separate the frame members from the inner member, fillets of material being left to hold the partly formed billet rigidly in one piece, forming four identical inner apertures on a common radius from the z axis, two lying on the x axis and two on the y axis to provide access to inner regions of the pivot means after insertion in their bores, forming four identical outer apertures on a common radius from the z axis, two lying on the x axis and two on the y axis to provide access to outer regions of the pivot means after insertion in their bores, forming an intermediate annular slot between the inner and outer annular slots, again co-axially with the z axis, the intermediate slot being in four identical segments two being equally spaced about the x axis and two being equally spaced about the y axis to provide eventual separation between the inwardly and outwardly directed regions of the first and second frame members, inserting and anchoring pivot means in the four bores to provide pivots between the inner member and the frame members and between the outer member and the frame members, and, removing the fillets of solid material to release the frame members from one another and from the outer and inner members.
 5. A method of forming a gimbal assembly according to claim 4 wherein a bore is formed along the z axis.
 6. A method of forming a gimbal assembly according to claim 4 wherein the pivot means are formed as four sets of axially joined pairs of pivot units, each pair of units being inserted in one of said bores and subsequently separated to form separate pivot ends. 